1. Field of the Invention
This device relates to apparatus attachable to a door for preventing the door from being opened.
2. Description of the Prior Art
A typical door is mounted in a door jamb with hinges which are attached to the mounting edge of the door. The door pivots along the mounting edge within the doorway defined by the door jamb. The door has an open position for permitting passage through the doorway and a closed position for prohibiting passage through the doorway.
The typical door incorporates a standard door latching assembly for maintaining the door in the closed position. The standard latching assembly usually includes a sliding bar which is operable to extend perpendicularly from the latching edge of the door, the latching edge generally being the edge opposite the mounting edge. In the latching position, the sliding bar extends from the latching edge into an aperture in a strike plate attached to the latching surface of the door jamb. The sliding bar may be connected to a door knob assembly having a shaft extending from one side of the door and a door knob attached to the shaft. The sliding bar is withdrawn from the aperture in the strike plate by rotation of the door knob and shaft.
To enable the door to be unlatched from either side, the door knob assembly can include a shaft and door knob extending from both sides of the door. The latching assembly can include a key lock or other locking system to prevent the door from being unlatched while the lock is engaged. The lock is engageable from the interior side of the door. Additionally, a key lock permits the door to be unlatched by the operation of a key from the exterior side of the door.
In many circumstances the standard door lock assembly is inadequate. Exterior key locks are susceptible to being opened by anyone having a master or skeleton key or by one skilled in the use of burglary tools. In certain circumstances, a person may have obtained an original or duplicate key for the lock. This is particularly true of a door lock for the door to an apartment, and can also be true for other doors. The problem of keys being in existence can be remedied by changing all of the door locks, but this is quite expensive, particularly if the change is intended to ensure security against only a very few persons. The general susceptibility of key locks to being opened is curable only by replacing or supplementing the existing locks with other devices.
Another familiar problem with the standard door latching assembly is the ease with which many of the sliding bars may be moved out of the strike plate aperture without operation of the door knob assembly. As a door is pivoted to the closed position, the sliding bar must pass across the strike plate on one side of the aperture. The sliding bar is normally held in the extended latching position. The sliding bar is therefore provided with a convex curved leading surface which first contacts the strike plate when the door is closed and which causes the bolt to be forced into the door until the door is fully closed. The sliding bar is then free to return to the extended position, and the sliding bar extends into the aperture in the strike plate latching the door. This curved leading surface thus facilitates closing and latching the door. However, it also facilitates opening the door by direct removal of the sliding bar from the aperture in the strike plate. This may be accomplished by insertion of a thin object such as a knife into the space between the latching edge of the door and the latching surface of the door jamb. Forcing this object against the sliding bar will force the sliding bar into the door and out of the aperture, in the same manner that the sliding bar is temporarily forced into the door when the door is closed.
Another problem with the standard door latching assembly, as well as other latching systems, is that they are easily released from inside the door. Although this feature makes such devices more convenient to use, it decreases their usefulness in some circumstances. The primary problem arises if the door includes or is located near a glass window. The glass may be easily broken and a hand reached in to disengage the latch.
In addition, a latch may be desired which can be used from the exterior of the doorway. It is obviously important then to have a device which cannot be disengaged without first disengaging a locking system operably connected with the latching assembly.
In recognition of the desirability of improved door latching systems, various door attachments have been devised. A door lock attachment should be effective, inexpensive, easily installed, and not damaging to the door or its surrounding structure. None of the present devices meet all of these criteria.
One type of device involves the operable attachment of additional sliding bars to the door knob assembly. Examples of these devices are disclosed in U.S. Pat. Nos. 1,172,846 issued to Swanson on Feb. 22, 1916; 1,240,403 issued to Amato on Sept. 18, 1917; and 2,188,532 issued to Dominguez on Sept. 24, 1938. Each of these devices incorporate two vertical sliding bars, one extending to the floor and the other extending to the door jamb above the door. These devices are notably expensive, difficult to install, and rather unsightly. Since they operate in conjunction with the standard door latching assembly, they also share equally its shortcomings.
A second type of device is exemplified by the apparatus claimed in U.S. Pat. No. 3,583,743 issued to Newell on June 8, 1971. The apparatus includes a vertical, adjustable-length member which engages the bottom of the shaft of the door knob assembly and the floor. Characteristic of this type of device, the Newell apparatus is relatively expensive, can be used only on the interior of the door, and must be modified for use with various floor coverings.
A third type of device involves a locking bolt which is attached to the door and passes through an aperture in a plate attached to the door jamb. Examples of this type of locking assembly are the chain lock having a bolt received in a channel attached to the door jamb, and a bolt which slides in a channel attached to the door and is received within an aperture in a retaining member located on the door jamb. In each of these devices, one or both of the locking elements is attached to the interior side of the door or door jamb, usually by screws. This results in the lock being only as strong as the screws which hold it in place. Frequently, it is one of the locking elements being dislodged from the door or door jamb which permits the door to be forced open. Further, these devices must be permanently affixed to the door and door jamb, and they may be disengaged by a hand reached through a nearby broken window.
Another device of this general type is disclosed in U.S. Pat. No. 1,239,882 issued to Macbeth on Sept. 11, 1917. This device incorporates a locking bolt having a hooked end extending around one side of the door knob shaft. The other end is passed through two holes in the retaining plate. This plate has gripping fingers which are shaped to be embedded in the door jamb when force is applied to the plate in the direction of the door. This force is applied by a wing nut which is threaded onto the end of the locking bolt which passes through the holes in the plate. When the nut is tightened against the portion of the plate forming the aperture farthest from the door, this exerts tension through the plate and the locking bolt to the door knob shaft and the gripping fingers. As the nut is tightened, the gripping fingers become embedded in the door jamb.
Like the previous locking devices discussed, this device has many undesirable aspects. Most significant is the manner in which the door is secured against being opened. When pressure is exerted to open the door, the force is fully borne by that portion of the door jamb engaged by the gripping fingers. The device is therefore initially limited to the strength of the door jamb material so engaged and the strength of the attachment of the jamb to the wall. The device would clearly be useless if the door jamb is merely a thin piece of wood nailed to the wall or if the door jamb were metal. Further disadvantages of this device include the damage done to the door jamb, the susceptibility of the device to being released by a hand reached through a nearby, broken window, and the needless expense and unsightliness of the design. The device is also not suited for use on the exterior of the door.